A variety of dental implants currently are known and available. The implants are designed for insertion into the mandible or jawbone of a patient to support the mounting of a prosthesis. Generally, a cylindrical hole is formed in the mandible or jawbone of the patient, and the implant is disposed in the hole and allowed to undergo osseointegration.
A typical threaded dental implant has a generally cylindrical body with an unthreaded, annular portion at its proximal end. The remaining external surface of the generally cylindrical body is substantially threaded. The threads allow the dental implant to be turned into the cylindrical hole formed in the jawbone of the patient. The threads also secure the dental implant and promote osseointegration.
Insertion of the dental implant into the patient's jawbone may be simplified by the use of self-tapping implants. Such implants include self-tapping features often located at the distal end of the implant. Such features include, for example, recesses, such as flutes, that extend generally axially along the side wall of the distal end. The recesses interrupt the threads at the distal end and create cutting edges able to cut into the bone tissue along the periphery of the cylindrical hole formed in the jawbone. The recesses also provide spaces for holding any bone fragments or other tissue displaced during insertion of the implant.
Self-tapping implants are desirable because they immediately form a secure mechanical attachment to the bone tissue. They also promote direct integration of the bone tissue with the implant, i.e. osseointegration, through the more intimate contact formed as the self-tapping implant is threaded into the bone tissue.
Another aid to osseointegration is the use of a bio-reactive material as a coating on the implant. The implant may be made from a metallic material, such as titanium or a titanium alloy, to provide strength. This metallic material then may be coated with a material that promotes integration of the implant and surrounding bone tissue.
One bio-reactive agent that has been very successful in promoting osseointegration is hydroxylapatite (HA). HA is a synthetic form of biological apatite that is one of the major compounds occurring in human bones and teeth. Thus, it would be desirable to coat the outer surface of the implant with HA at least to the extent the implant is inserted into the bone tissue.
The use of bio-reactive materials, however, has been particularly problematic with self-tapping implants. As discussed by the inventor in U.S. Pat. No. 5,571,017, the cutting edges of the self-tapping implant must be sharp enough to shave bone chips. However, coating the self-tapping distal end with a bio-reactive material, such as HA, requires that the surface be substantially roughened by, for instance, blasting it with an aluminum oxide blast media. Blasting with aluminum oxide, however, rounds the cutting edges of the self-tapping features. This reduces the cutting efficiency of the self-tapping cutting edges. When this efficiency is reduced, greater torques are required to insert the implant, particularly when inserted into dense bone. The added torque can cause damage, including damage to the implant itself.
Additionally, the ceramic particles of the aluminum oxide blast media cannot readily be dissolved in solutions, such as acid solutions, or otherwise removed. This leaves particles between the metallic core material and the bio-reactive coating. The particles substantially reduce the bond or tensile strength between the metallic core and the bio-reactive coating, which can lead to fractured coatings, especially when subjected to the increased torques.
As disclosed in U.S. Pat. No. 5,571,017, an attempt has been made to overcome this problem by providing a relatively smooth, metallic distal end having self-tapping features that are free from any bio-reactive material. Only the middle portion of the dental implant, disposed between the proximal end and the self-tapping distal end, is provided with a relatively rough surface, such as by HA coating. This solution, however, does not permit coating of the dental implant with a bio-reactive material throughout the entire area of desired integration between bone tissue and implant.
It would be advantageous to be able to promote osseointegration along the entire surface area of the implant, when inserted into bone tissue, without creating the potential for damage by increased torques placed on the implant or fragile coatings.